Semiconductor light emitting device having nanostructure porous silicon and mesostructure porous silicon

ABSTRACT

At least a one conductivity type nanostructure PS layer whose thickness is controlled, and the opposite conductivity type nanostructure PS layer and a one conductivity type mesostructure PS layer arranged in contact with both these sides are comprised. Since the one conductivity type nanostructure PS layer is formed by anodizing the non-degenerate n-type crystalline silicon layer whose thickness is established in advance, the thickness which can provides a maximum luminescence efficiency can be obtained correctly. Then a semiconductor light emitting device whose luminescence efficiency is improved without increasing an unnecessary series resistance is provided. An inexpensive semiconductor light emitting device having a large light emitting area can be provided, since silicon wafer having a large diameter can be employed as the material for light emission

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor light emitting deviceused in an optoelectronic integrated circuit and an image displaydevice, and more particularly to a semiconductor light emitting deviceand a method for manufacturing the same using a porous silicon.

2. Description of the Related Art

The porous silicon (hereinafter referred to as a "PS") differs from acrystalline silicon (hereinafter referred to as a "c-Si") in opticalproperties, and absorption edge energy generally becomes large.Moreover, electrical properties also changes, and the resistivitybecomes high as compared with the original c-Si. Three kinds of PSs areknown as follows:

(a) Nanostructure PS:

The PS of which a porosity is 20 to 80% and the diameter of microporousholes is not more than approximate 2 nm is referred to as "ananostructure PS". Differing from the c-Si, the nanostructure PS showsluminescence in a visible-light range. Pumping this nanostructure PS bythe shorter wavelength light within the spectral region from blue toultra violet, photoluminescence (PL) of a luminescence efficiency(external quantum efficiency) of approximate 10% at the maximum can beobserved. Moreover, electroluminescence (EL) can be obtained also byinjecting current into the nanostructure PS.

(b) Mesostructure PS:

On the other hand, the PS of which the porosity is 40 to 60% and thediameter of the microporous holes is approximate 2 to 50 nm is referredto as "a mesostructure PS". The luminescence efficiency of themesostructure PS is generally low as compared with the nanostructure PS,and an emission wavelength also generally comes to the longer wavelengththan the nanostructure PS. The mesostructure PS is coarse in structureas compared with the nanostructure PS and is low in resistivity ascompared with the nanostructure PS.

(c) Macrostructure PS:

Moreover, a PS of which the porosity is further low than themesostructure PS and the diameter of the microporous holes is 50 nm ormore is referred to as "a microstructure PS". The macrostructure PS canhardly emit light and is further low in resistivity as compared with themesostructure PS.

These PSs are formed by anodization, or by feeding a current inwardlyfrom the surface of the silicon through the c-Si (single crystal siliconor polycrystalline silicon) as electrodes in the solution containinghydrogen fluoride (HF). Moreover, as a cathode, materials such asplatinum (Pt) being usually not dissolved into an anodization solutionis used. Although the PS and the material having the structure similarthereto can be made by other methods, they are omitted because of beingnot important in the invention.

Thus, the PS is constituted by the number of the microporous holes ofthe diameter of approximate 1 to 100 nm, remained small c-Si particlesor a skeleton, and an amorphous portion surrounding thereabouts. Bychanging the conditions such as the conductivity type and resistivity ofthe original c-Si, the current density at anodizing, the composition ofthe anodization solution, the presence or absence of light irradiationand the intensity of the light irradiation, the structure of the PSbeing made is changed, whereby the nanostructure PS, the mesostructurePS or the macrostructure PS can be obtained.

For example, the nanostructure PS is obtained by anodizing the c-Sicontaining a p-type impurity doped to the extent being not degenerated(a non-degenerate p-type). Moreover, the nanostructure PS is obtainedalso by anodization while irradiating a non-degenerate n-type c-Si of alow impurity concentration with light. This nanostructure PS is fine sothat the porosity is approximate 20 to 80% and the diameter of the holesis not more than 2 nm. That is, since remaining c-Si particles or a sizeof the skeleton are fine, the resistivity becomes high as compared withthat of the original c-Si. For example, the nanostructure PS can beobtained by anodizing the degenerate p-type c-Si or the degeneraten-type c-Si, containing the p-type or n-type impurity with higherimpurity concentration so that the Fermi level is located within thevalence or conduction band. For example, the macrostructure PS can beobtained by anodizing the non-degenerate n-type c-Si in a darkroom.

The above-noted description of the three kinds of PSs which differ instructure is performed on the generalized characteristics of therespectively typical one, and actually, there are the PSs having thecharacteristic intermediate between the mesostructure PS and thenanostructure PS and the PSs having the characteristic intermediatebetween the mesostructure PS and the macrostructure PS or the like.Moreover, for example, even the PS belonging to the same nanostructurePS can differ in the fine structure in some cases depending upon thedifference of a conductivity type of the original c-Si. Moreover, eventhough the original c-Si is uniform, the PS of which the structurediffers in the direction of a depth can be made depending upon anodizingconditions. Furthermore, even the PS belonging to the mesostructure PSor the macrostructure PS as the general structure and characteristic,the PS containing the nanostructure PS can be made partially in themicroscopic portion depending upon the anodizing conditions.

Therefore, when making a light emitting device using the PS, asufficient consideration should be taken in the both sides of theelement design from the viewpoint of by which structure PS a layer isconstituted and for what it is used, and a selection of a method formaking the element structure.

It is reported in the proceedings of the 44 th Japan Society of AppliedPhysics and Related Society Symposium, No.2, P.806, Section a-B-6,"Characteristics of a pn-junction type photoanodically fabricated poroussilicon LED", by Nishimura, Nagao and Ikeda that external quantumefficiency of the EL luminescence comes to approximate 1% at the maximumin the light emitting device using the PS (hereinafter referred to as a"PS light emitting device"). This PS light emitting device is made bypreparing a c-Si wafer that the p⁺ type c-Si layer is formed on then-type c-Si substrate to anodize the surface of this c-Si wafer underthe irradiating with light using a lamp. When anodizing under suchconditions, the p⁺ type c-Si layer of the surface of which resistivityis low becomes the mesostructure PS layer and the n-type c-Si substrateportion of the area which no light from the lamp reaches becomes themacrostructure PS. In FIG. 1 and FIG. 2, the structure and the equipmentfor manufacturing this PS light emitting device are shown.

Referring to FIG. 1, the macrostructure PS layer 63 made from the n-typec-Si, hereinafter referred to as "a n-type macrostructure PS layer 63",is formed on a n-type c-Si substrate 64. And the nanostructure PS layer62 made from the n-type c-Si, hereinafter referred to as "a n-typenanostructure PS layer 62" is formed on the n-type macrostructure PSlayer 63. And farther the mesostructure PS layer 61 made from the p⁺type c-Si, hereinafter referred to as a p-type mesostructure PS layer,is formed thereon. Moreover, the expressions of "the n-typemacrostructure PS layer", "the n-type nanostructure PS layer", "thep-type mesostructure PS layer" or the like are expressed for convenienceand differ from the n-type and the p-type in the c-Si. The reason why isthat, generally, in the PS layer, acceptor impurities and donorimpurities are inactivated at room temperature. A translucent goldelectrode 66 which serves as an anode is formed on the p-typemesostructure PS layer 61 and an aluminum electrode 65 which serves as acathode is formed on the back of the n-type c-Si substrate 64. A directcurrent power supply 67 for the EL is connected between the anode 66 andthe cathode 65. In the structure shown in FIG. 1, the n-typenanostructure PS layer 62 acts as an EL actve layer. Moreover, thep-type mesostructure PS layer 61 has a function to form a junctionsimilar to the pn-junction in the c-Si (hereinafter, such kind ofjunction by the PS layer is referred to as a "the pn-junction" forconvenience) between the n-type nanostructure PS layer 62 and the p-typemesostructure PS layer 61, and a function to get better ohmic contactwith the translucent gold electrode 66 formed on the layer 61.

In order to form the structure shown in FIG. 1, first, a c-Si wafer 7 onwhich a p⁺ type c-Si layer 71 of 0.6 μm in thickness and resistivity of2×10⁻³ Ω-cm is formed on a surface of a n-type c-Si substrate 72 of 500μm and resistivity of 5 Ω-cm using a thermal diffusion method isprepared. Subsequently, it can be manufactured by anodizing this c-Siwafer 7 as shown in FIG. 2. That is, as shown in FIG. 2, a container 1for anodization, which is made of polytetrafluoroethylene(PTFE), havingan opening on the bottom is contacted closely with the surface of the p⁺type c-Si layer 71 using O-rings 2 to fill an anodizing mixed solutionconsisting of hydrofluoric acid and ethyl alcohol 4 into this containermade of PTFE 1. Because of using the O-ring 2, the anodizing mixedsolution consisting of hydrofluoric acid and ethyl alcohol 4 does notleak from the bottom of the container 1 made of PTFE. The anodizationsolution 4 consists of hydrofluoric acid of 50 weight percent and ethylalcohol of 99.9 weight percent mixed at a volume ratio of 1:1. In theanodizing mixed solution consisting of hydrofluoric acid and ethylalcohol 4, a platinum electrode 3 is arranged. On the other hand, on theback of the n-type c-Si substrate 72, the aluminum electrode 65 whichwill become the cathode shown in FIG. 1 eventually, and a desiredanodizing current is fed through the anodizing mixed solution consistingof hydrofluoric acid and ethyl alcohol 4 by the variable direct currentpower supply 6 connected between the platinum electrode 3 and thealuminum electrode 65. The anodizing is performed while irradiating thep⁺ type c-Si layer 71 and the n-type c-Si substrate 72 thereunder by atungsten lamp 5 arranged on the upper of the container made of PTFE 1.Therefore, the platinum electrode 3 is arranged such that the lightradiated from the tungsten lamp 5 can not be impeded to reach thesurface of the c-Si wafer 7.

The mesostructure PS layer 61 is obtained by anodizing the p⁺ type c-Silayer 71 shown in FIG. 1. Moreover, the nanostructure PS layer 62 shownin FIG. 1 is formed at the portion in proximity to the surfaceinfluenced by light radiation in the n-type c-Si substrate 72 shown inFIG. 2. Moreover, the macrostructure PS layer 63 is formed at a slightlyinner portion from the surface not influenced by light radiation in then-type c-Si substrate 72. The n-type c-Si substrate 64 shown in FIG. 1is a portion remaining as the c-Si of the n-type c-Si substrate 72 shownin FIG. 2. According to the method shown in FIG. 2, the longer ananodization time is, the thicker the nanostructure PS layer 62 becomes,and moreover, the macrostructure PS layer 63 formed thereunder comes tobe thick increasingly in response thereto. Moreover, the anode 66 shownin FIG. 1 is the translucent gold electrode formed by evaporating a goldthin film by a vacuum evaporation method after anodizing.

The luminescence efficiency (the quantum efficiency) depends upon a wayof anodizing and the anodization time, thereby not always beingconstant. Generally, the nanostructure PS layer anodized sufficiently byextending the anodization time has higher luminescence efficiency thanthat of the nanostructure PS layer anodized insufficiently with theshorter anodization time.

To some extent, the longer the anodization time becomes, the higher theexternal quantum efficiency and higher the electric power efficiency ofthe PS light emitting device become. The reason why is that when theanodization time is made long, so that anodizing is promotedsufficiently, the quantum efficiency increases. However, when theanodization time is long excessively, the electric power efficiencydecreases again. This reason why is that, although the external quantumefficiency becomes higher owing to the increase of the thickness of thenanostructure PS layer 62 being the light emitting layer in company withthe increase of the anodization time, the increase of the seriesresistance of the nanostructure PS layer whose resistivity is highbecomes prominent when exceeding a certain thickness. This is to beunderstood by referring to FIG. 3. That is, FIG. 3 shows a relationshipbetween a series resistance Rs of such PS light emitting device and athickness "d" of the nanostructure PS layer 62. Referring to FIG. 3, asymbol of O shows the series resistance Rs of the light emitting devicehaving the n-type nanostructure PS layer 62 shown in FIG. 1. And asymbol of ⋄ shows the series resistance Rs of the light emitting device,in which a luminescence layer is constituted by the p-type nanostructurePS layer made from the p-type c-Si, having the approximately sameelement structure as that shown by the symbol of O. It is understoodthat there is a relationship of approximately Rsd²˜3. Therefore, for thelight emitting device whose external quantum efficiency is high, theseries resistance thereof becomes high inevitably. Especially, theseries resistance Rs of the PS light emitting device, whose externalquantum efficiency is high as 0.1 to 1%, becomes high as 100 k Ω to 1MΩ, and a high supply voltage is required in order to inject a currentinto such PS light emitting device. That is, electric energy convertedto thermal energy is more increased with respect to electric energyconverted to light energy, whereby the electric power efficiency wouldbe decreased.

SUMMARY OF THE INVENTION

The present invention is devised for solving the problems of the priorart described above, and the object of the invention is to reduce aseries resistance Rs of a PS light emitting device to improve anelectric power efficiency without impairing external quantum efficiency.

The further object of the invention is to provide a light emittingdevice of which an operation voltage is low and an external quantumefficiency is high.

The another object of the invention is to provide a method formanufacturing a PS light emitting device of which control of a filmthickness of the luminescence layer is easy and the external quantumefficiency and an electric power efficiency are high.

The additional object of the invention is to provide a method formanufacturing the PS light emitting device which can be integratedreadily on the same silicon substrate with other electronic devices andcan be manufactured inexpensively.

To accomplish the object described above, a first feature of theinvention is a semiconductor light emitting device at least comprising afirst one conductivity type nanostructure porous silicon (PS) layer, anopposite conductivity type mesostructure PS layer disposed on the firstone conductivity type nanostructure porous silicon (PS) layer, and afirst one conductivity type mesostructure PS layer formed under thefirst one conductivity type nanostructure PS layer. Where "the oneconductivity type nanostructure PS layer" is an abbreviated expressionof the nanostructure PS layer formed from the one conductivity typecrystalline silicon (c-Si) and "the opposite conductivity typemesostructure PS layer" is an abbreviated expression of themesostructure PS layer formed from the opposite conductivity type c-Si.Here, if the one conductivity type is n-type, the opposite conductivitytype is p-type. And, if the one conductivity type is p-type, theopposite conductivity type is n-type. Moreover, "the one conductivitytype mesostructure PS layer" is an abbreviated expression of themesostructure PS layer formed from the one conductivity type c-Si.Although the one conductivity type nanostructure PS layer is the layerwhich functions as the main light emitting layer, the resistivity ishigh. On the other hand, the luminescence efficiency and the resistivityof the first one conductivity type mesostructure PS layer are low. "Thenanostructure PS layer" implies the PS layer of which the porosity is 20to 80% and the diameter of microporous holes is not more thanapproximate 2 nm as described above. On the other hand, "themesostructure PS layer" implies the PS layer of which the porosity is 40to 60% and the diameter of microporous holes is not more thanapproximate 2 to 60 nm as described above. The pn-junction is formedbetween the first one conductivity type nanostructure PS layer and theopposite conductivity type mesostructure PS layer, and carriers areinjected from the opposite conductivity type mesostructure PS layer tothe first one conductivity type nanostructure PS layer, thereby lightbeing emitted.

The first one conductivity type nanostructure PS layer according to theinvention may be formed by anodizing the non-degenerate crystallinesilicon (c-Si) layer whose impurity concentration is low. That is, whenanodizing the structure that the one conductivity type non-degeneratec-Si layer is sandwiched between the opposite conductivity typedegenerate c-Si layer whose impurity concentration is high and the firstone conductivity type degenerate c-Si layer, only the one conductivitytype degenerate c-Si layer becomes the nanostructure PS layer, whereby athickness can be controlled correctly. That is, according to a firstfeature of the invention, the thickness of the first one conductivitytype nanostructure PS layer which serves as the light emitting layer canbe controlled into the predetermined thickness that the seriesresistance Rs is not increased and the maximum luminescence efficiencycan be obtained. Conversely, the thickness of the eventual first oneconductivity type nanostructure PS layer is limited within thepredetermined thickness, whereby, at anodizing, the sufficientanodization time can be expended to anodize sufficiently. That is tosay, the nanostructure PS layer in the first feature of the invention isin the state that "transformation of crystalline silicon to poroussilicon" has promoted sufficiently, and so to speak, the layer is thecompleted nanostructure PS layer. Therefore, according to the firstfeature of the invention, the light emission from this completednanostructure PS layer is utilized, whereby the luminescence efficiency(the quantum efficiency) is extremely high as compared with theuncompleted nanostructure PS layer in the prior art.

In the first feature of the invention, it is preferable to furthercomprise at least a second one conductivity type nanostructure PS layerand a second one conductivity type mesostructure PS layer under thissecond one conductivity type nanostructure PS layer on the lower of thefirst one conductivity type mesostructure PS layer. "The second oneconductivity type" is the same conductivity type as the first oneconductivity type. The second one conductivity type nanostructure PSlayer also is the completed nanostructure PS layer. As is describedusing FIG. 3, since the series resistance Rs of the nanostructure PSlayer is proportional to the square or the cube of the thickness "d" ofthe nanostructure PS layer, the series resistance becomes low suddenlywhen thinning the thickness of the nanostructure PS layer. Therefore,when connecting a plurality of thin nanostructure PS layers (N layers,defining N as a positive integer) in series, the total series resistanceRs (the total) becomes small value.

For example, the n-type nanostructure PS layers having the thickness ofa fraction of N of the nanostructure PS layer of a single layer areprepared by N layers to form a stacked structure that the n-typemesostructure PS layers of N-1 layers are sandwiched between these Nlayers. In this case, since the resistivity of the mesostructure PSlayer is extremely low as compared with that of the nanostructure PSlayer, it hardly contributes to the series resistance. Therefore, thetotal series resistance Rs.sub.(total) of this stacked structure isreduced to a fraction of N as compared with that of the single layer ofthe n-type nanostructure PS. That is, when investigating the thicknessof each layer of the nanostructure PS layer divided into the multi-layersuch that the thickness of the total of N layers becomes the same as thethickness of the nanostructure PS layer of a single layer, lightemitting intensity is approximately equal since both the thickness areequal as a whole, but the series resistance is reduced drastically dueto the stacked structure. Therefore, the increase in efficiency of theelectric power efficiency can be attained by the reduced seriesresistance. Moreover, the light emitting can be performed by a loweroperating voltage.

A second feature of the invention relates to a method for manufacturingthe semiconductor light emitting device according to the described-abovefirst feature. That is, the second feature of the invention is a methodfor manufacturing the semiconductor light emitting device comprising thesteps of: at least preparing a c-Si wafer comprising: at least the firstone conductivity type degenerate crystalline silicon (c-Si) layer; thefirst one conductivity type non-degenerate c-Si layer formed on thefirst one conductivity type degenerate c-Si layer; and the oppositeconductivity type degenerate c-Si layer formed on the first oneconductivity type non-degenerate c-Si layer, and anodizing this c-Siwafer to transform the first one conductivity type non-degenerate c-Silayer to the first one conductivity type nanostructure PS layer. In thiscase, since the first one conductivity type degenerate c-Si layer andthe opposite conductivity type degenerate c-Si layer are the c-Si layerswhose impurity concentration are high and are transformed to themesostructure PS layers respectively by anodization. Since the thicknessof the first one conductivity type non-degenerate c-Si layer, whoseimpurity concentration is low, is defined correctly by an epitaxialgrowth method or the like, the thickness of the first one conductivitytype non-degenerate c-Si layer is transformed to the thickness of thefirst one conductivity type nanostructure PS layer automatically andexactly, and can not be made thicker than this thickness, whereby athickness can be controlled correctly. A degenerate c-Si substrate maybe used as the first one conductivity type degenerate c-Si layer.Moreover, according to the second feature of the invention, even thoughthe anodization time is extended sufficiently, the thickness of thefirst one conductivity type nanostructure PS layer can not be increased,whereby the promotion of "transformation of crystalline silicon toporous silicon" can be made sufficiently. In the prior art, when thepromotion of "transformation of crystalline silicon to porous silicon"is made, "transformation of crystalline silicon to porous silicon" isinitiated from the top surface side, whereby the degree of the promotionof "transformation of crystalline silicon to porous silicon" is low inthe portion far from the top surface, so that the nanostructure havinglow luminescence efficiency is formed. Moreover, although there has beena disadvantage that the thickness thereof also is made thick more thanrequired in the prior art, according to the second feature of theinvention, the completed nanostructure PS layer whose luminescenceefficiency is high can be formed uniformly in the direction of athickness. Moreover, according to the prior art, since a certainthickness is required in order to make progress of "the transformationof crystalline silicon to porous silicon" sufficiently, thinning isdifficult. On the other hand, according to the second feature of theinvention, even in the case of an extremely thin film thickness,transformation to the completed nanostructure PS layer can be performedeasily and thinning also can be performed.

In the first feature, it has been mentioned that the series resistancefurther is reduced by transforming the nanostructure PS to amulti-layered structure. Therefore, in order to form the multi-layerednanostructure PS layer, in the second feature of the invention, the PSwafer comprises the second one conductivity type non-degenerate c-Silayer formed under the first one conductivity type degenerate c-Silayer; and further the second one conductivity type degenerate c-Silayer therebelow, and the second one conductivity type non-degeneratec-Si layer may be transformed to the second nanostructure PS layer byanodization. Furthermore, it is as a matter of course that by taking thestructure that a second and a third one conductivity type non-degeneratec-Si layers and the degenerate c-Si layer are laminated alternately, thefurther multi-layered structure can be realized. The degenerate c-Sisubstrate may be used as the lowest degenerate c-Si layer.

Anodizing in the second feature of the invention may be performed bymaking contact the opposite conductivity type degenerate c-Si layerbeing positioned on the top layer of the described-above c-Si wafer withthe anodization solution containing hydrogen fluoride; providing a metalelectrode on a bottom surface of the c-Si wafer; and feeding a currentthrough this electrode and the electrode provided in the anodizationsolution containing hydrogen fluoride.

In this case, when the one conductivity type is n-type (and the oppositeconductivity type is p-type), anodizing is preferably performed whileirradiating light.

According to the first and second features of the invention, the maximumluminescence efficiency can be secured, and a manufacturing yield of thesemiconductor light emitting device becomes high and the productivity isimproved.

Moreover, in the first and second feature of the invention, it is as amatter of course that the c-Si may be either single crystal silicon andpolycrystalline silicon.

Other and further objects and features of the present invention willbecome obvious upon an understanding of the illustrative embodimentsabout to be described in connection with the accompanying drawings orwill be indicated in the appended claims, and various advantages notreferred to herein will occur to one skilled in the art upon employingof the invention in practice.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view showing an example of a structure of asemiconductor light emitting device using the prior PS.

FIG. 2 is a schematic view describing an equipment for manufacturing asemiconductor light emitting device shown in FIG. 1

FIG. 3 is a view showing a relationship between a thickness and a seriesresistance of a nanostructure PS layer.

FIG. 4 is a sectional view showing a structure of a semiconductor lightemitting device according to a first embodiment of the invention.

FIG. 5 is a schematic view describing an equipment for manufacturing asemiconductor light emitting device according to a first embodiment ofthe invention.

FIG. 6 is a sectional view showing a structure of a semiconductor lightemitting device according to a second embodiment of the invention.

FIG. 7 is a schematic view describing an equipment for manufacturing asemiconductor light emitting device according to a second embodiment ofthe invention.

FIG. 8 is a view showing relationships between an external quantumefficiency and series resistance of each of a semiconductor lightemitting device according to a first and a second embodiment of theinvention and the prior art.

FIG. 9A is a schematic view of a display device using a silicon wafer of300 mm φ in diameter according to a third embodiment of the invention.

FIG. 9B is a block diagram showing a constitution of a display deviceshown in FIG. 9A.

FIG. 9C is a schematically sectional view showing a LED matrix section.

FIGS. 10A to 10S are schematically process-sectional views describing amethod for manufacturing a LED display device according to a thirdembodiment of the invention.

FIG. 11 is a schematic view describing an another method formanufacturing a LED display device according to a third embodiment ofthe invention.

FIG. 12 is a schematically sectional view showing a LED matrix sectionaccording to a modification of a third embodiment of the invention.

FIG. 13 is a schematically sectional view showing a part of an interiorillumination device according to an another embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Various embodiments of the present invention will be described withreference to the accompanying drawing. It is to be noted that the sameor similar reference numerals are applied to the same or similar partsand elements throughout the drawings, and the description of the same orsimilar parts and elements will be omitted or simplified.

Generally and as it is conventional in the representation ofsemiconductor devices, it will be appreciated that the various drawingsare not drawn to scale from one figure to another nor inside a givenfigure, and in particular that the layer thickness are arbitrarily drawnfor facilitating the reading of the drawings.

First Embodiment

FIG. 4 shows a structure of a semiconductor light emitting deviceaccording to a first embodiment of the invention. As shown in FIG. 4, inthe semiconductor light emitting device according to a first embodimentof the invention, the n-type mesostructure PS layer (the first oneconductivity type mesostructure PS layer) 13, the n-type nanostructurePS layer (the first one conductivity type nanostructure PS layer) 12 of2 μm in thickness and the p-type mesostructure PS layer (the oppositeconductivity type mesostructure PS layer) 61 of 0.6 μm in thickness areformed in order on a n⁺ type c-Si substrate 14. On the p-typemesostructure PS layer 61, the translucent gold electrode 66 whichserves as the anode is formed and on the back of the n⁺ type c-Sisubstrate 14, the aluminum electrode 65 which serves as the cathode isformed. The direct current power supply 67 for the EL is connectedbetween the anode 66 and the cathode 65. The thickness of the n-typenanostructure PS layer 12 acting as the EL actve layer is controlledinto the thickness required from a design viewpoint correctly. And thepromotion of "transformation of crystalline silicon to porous silicon"0is performed sufficiently, so that the n-type nanostructure PS layer 12becomes the completed nanostructure PS layer. That is, it will beapparent from the description of the manufacturing method describedbelow that the n-type nanostructure PS layer 12 is the layer that thenon-degenerate n-type c-Si layer is transformed into a porous layer andthe thickness of the n-type nanostructure PS layer 12 is controlled bythe thickness of the non-degenerate n-type c-Si layer correctly.

The p-type mesostructure PS layer 61 has a function to form thepn-junction between the n-type nanostructure PS layer 12 and the p-typemesostructure PS layer 61. Further, the p-type mesostructure PS layer 61has a function to get better ohmic contact with the translucent goldelectrode 66 formed on the p-type mesostructure PS layer 61.

FIG. 5 shows a method for manufacturing a semiconductor light emittingdevice according to a first embodiment of the invention.

(a) First, as shown in FIG. 4, a c-Si wafer 8 on which thenon-degenerate n-type c-Si layer (the first one conductivity typenon-degenerate c-Si layer) 22 of 2 μm in thickness and resistivity of 1Ω-cm and the degenerate p⁺ type c-Si layer (the opposite conductivitytype degenerate c-Si layer) 71 of 0.6 μm in thickness and resistivity of2×10⁻³ Ω-cm are formed on the degenerate n⁺ type c-Si substrate (thefirst one conductivity type degenerate c-Si layer) 23 of 500 μm andresistivity of 1×10⁻³ Ω-cm by epitaxial growth is prepared.

(b) Secondly, the aluminum electrode 65 is formed on the back of thedegenerate n⁺ type c-Si substrate 23 using a vacuum evaporation methodor a sputtering method. Thereafter, sintering is performed at 400 to450° C. to get better ohmic contact of the aluminum electrode 65 toreduce the contact resistance.

(c) Thereafter, as shown in FIG. 5, a container 1 having an opening onthe bottom, which is made of PTFE, is contacted closely with the surfaceof the c-Si wafer 8 using O-rings 2 to fill the anodizing mixed solutionconsisting of hydrofluoric acid and ethyl alcohol 4 into this containermade of PTFE 1. Since using the O-ring 2, the anodizing mixed solutionconsisting of hydrofluoric acid and ethyl alcohol 4 does not leak fromthe bottom of the container made of PTFE 1. The anodization solution 4consists of hydrofluoric acid of 50 weight percent and ethyl alcohol of99.9 weight percent mixed at a volume ratio of 1:1. In the anodizingmixed solution consisting of hydrofluoric acid and ethyl alcohol 4, aplatinum electrode 3 is arranged. The tungsten lamp 5 is arranged on theupper of the container made of PTFE. Moreover, the platinum electrode 3is arranged such that the light radiated from the tungsten lamp 5 cannot be impeded to reach the surface of the c-Si wafer 8.

(d) Subsequently, a desired anodizing current of 30 mA/cm² is fed forsix minutes through the anodizing mixed solution consisting ofhydrofluoric acid and ethyl alcohol by the variable direct current powersupply 6 connected between the platinum electrode 3 and the aluminumelectrode 65. After adjusting the intensity of the light irradiationsuch that the intensity of the light irradiation at the surface of thec-Si wafer 8 becomes 2,000 lx to 200,000 lx, preferably approximate20,000 lx, anodizing is performed while irradiating with light by thetungsten lamp 5 arranged on the upper of the container made of PTFE 1.As a result, the degenerate p⁺ type c-Si layer 71 becomes the p-typemesostructure PS layer 61 by anodization. Moreover, a part of thedegenerate n⁺ type c-Si substrate 23 also is anodized in the same way tobecome the n-type mesostructure PS layer 13. On the other hand, thenon-degenerate n-type c-Si layer 22 becomes the n type nanostructure PSlayer 12 by anodization, whereby the laminated structure as shown inFIG. 4 is completed.

(e) Thereafter, after the container made of PTFE 1 or the like aredetached, gold film is evaporated up to a thickness to show translucenceon the surface of the p-type mesostructure PS layer 61 using vacuumevaporation method or the like. Referring to FIG. 5, the c-Si layeraround peripheral region would remain as it is, which not contact withthe anodization solution 4. Further, a part positioned therebelow is notanodized and is still remain as the c-Si layer. These peripheral regionremained as the c-Si layer is cut and removed using a diamond blade orthe like, whereby the fundamental structure of the semiconductor lightemitting device shown in FIG. 4 is completed. Thereafter, the processesof cutting into a die having a desired dimension and mounting on apredetermined lead flame or the like are the same as the process of theknown crystalline LED such as GaAs LED, GaAsP LED, AlGaAs LED, or GaPLED. Moreover, the aluminum electrode 65 used as the contact atanodizing is used as the cathode 65 of the semiconductor light emittingdevice according to the first embodiment. It is as a matter of coursethat the aluminum electrode 65 used in anodizing is removed once,metallic materials for the cathode may be deposited newly.

According to the method for manufacturing the described-abovesemiconductor light emitting device, in contrast to the PS lightemitting device and the method for manufacturing the same using theprior art shown in FIG. 1 and FIG. 2, the nanostructure PS is formedonly on the portion of the non-degenerate n-type c-Si layer 22, and allthe other portions becomes the mesostructure PS. Therefore, thethickness of the nanostructure PS layer 12 which is the light emittinglayer is controlled into the thickness required from a design viewpointcorrectly and "transformation of crystalline silicon to porous silicon"can be matured sufficiently.

As is mentioned above, there has been a disadvantage that although thethickness of the nanostructure PS is increased and the intensity of theEL becomes high when the anodization time becomes long to some extent,according to the prior art, the thickness of the nanostructure PSbecomes thick excessively in company with the lapse of the anodizationtime inevitably, so that the resistance is increased. In contrast withthis, when using the manufacturing method shown in FIG. 5, the thicknessof the n-type nanostructure PS layer 12 can not be grown excessivelyover the thickness (2 μm, in the first embodiment of the invention) ofthe non-degenerate n-type c-Si layer 22 laminated in advance, but themesostructure PS layer 13 whose resistivity is relatively low becomesthick even though the anodization time has lapsed beyond the timeforming the optimum thickness of the nanostructure PS layer. Therefore,the completed nanostructure PS layer having the high quantum efficiencycan be obtained by extending the anodization time sufficiently long tomake progress of "transformation of crystalline silicon to poroussilicon" sufficiently. Therefore, the thickness of the nanostructure PSlayer 12 can not be increased excessively even in the case that theexcessive anodization time has lapsed, as well as "transformation ofcrystalline silicon to porous silicon" which is necessary and sufficientto improve the quantum efficiency of the nanostructure PS layer 12 isstimulated and the thickness is secured, whereby the series resistanceRs of the light emitting device being made can not be increased by alarge amount than the value defined by the desired thickness of thenanostructure PS layer designed. Therefore, the semiconductor lightemitting device having the high quantum efficiency as designed can beprovided.

Second Embodiment

FIG. 6 shows a structure of a semiconductor light emitting deviceaccording to a second embodiment of the invention. As shown in FIG. 6,in the semiconductor light emitting device according to a secondembodiment of the invention, a fourth n-type mesostructure PS layer 13,a fourth n-type nanostructure PS layer 31, a third n-type mesostructurePS layer 32, a third n-type nanostructure PS layer 33, a second n-typemesostructure PS layer (the second one conductivity type mesostructurePS layer) 34, a second n-type nanostructure PS layer (the second oneconductivity type nanostructure PS layer) 35, a first n-typemesostructure PS layer (the first one conductivity type mesostructure PSlayer) 36, and a first n-type nanostructure PS layer (the first oneconductivity type nanostructure PS layer) 37 are formed in this order ona n⁺ type c-Si substrate 14. The thickness of the third to the firstn-type mesostructure PS layer 32, 34 and 36 is 0.1 μm respectively. Onthe other hand, the thickness of the fourth to the first n-typenanostructure PS layer 31, 33, 35 and 37 is 0.5 μm respectively. Thep-type mesostructure PS layer (the opposite conductivity typemesostructure PS layer) 61 of 0.6 μm in thickness further is formed onthe first n-type nanostructure PS layer 37. On the p-type mesostructurePS layer 61, the translucent gold electrode 66 which serves as the anodeis formed and on the back of the n⁺ type c-Si substrate 14, the aluminumelectrode 65 which selves as the cathode is formed. The direct currentpower supply 67 for the EL is provided between the anode 66 and thecathode 65. In the structure shown in FIG. 6, the fourth to the firstn-type nanostructure PS layer 31, 33, 35 and 37 act as the lightemitting layers and in this case, these thickness are controlled intothe thickness required from a design viewpoint correctly. That is, thefourth to the first n-type nanostructure PS layer 31, 33, 35 and 37 arethe layers that "transformation of crystalline silicon to poroussilicon" of the non-degenerate n-type c-Si layer whose impurityconcentration is low is made, and the thickness of the n-typenanostructure PS layer 12 is controlled by the thickness of thenon-degenerate n-type c-Si layer established in advance correctly, andthis thickness is controlled into the thickness required from a designviewpoint correctly and the promotion of "transformation of crystallinesilicon to porous silicon" is performed sufficiently so that the highquantum efficiency is shown. The p-type mesostructure PS layer 61 has afunction to form the pn-junction between the first n-type nanostructurePS layer 37 and the layer 61, and a function to get better ohmic contactwith the translucent gold electrode 66.

FIG. 7 shows a method for manufacturing a semiconductor light emittingdevice according to a second embodiment of the invention.

(a) First, as shown in FIG. 7, a c-Si wafer 9 on which a fourthnon-degenerate n-type c-Si epitaxial growth layer 41, a third degeneraten⁺ type c-Si epitaxial growth layer 42, a third non-degenerate n-typec-Si epitaxial growth layer 43, a second degenerate n⁺ type c-Siepitaxial growth layer (the second one conductivity type degenerate c-Silayer) 44, a second non-degenerate n-type c-Si epitaxial growth layer(the second one conductivity type non-degenerate c-Si layer) 45, a firstdegenerate n⁺ type c-Si epitaxial growth layer (the first oneconductivity type degenerate c-Si layer) 46, a first non-degeneraten-type c-Si epitaxial growth layer (the first one conductivity typenon-degenerate c-Si layer) 47, and a degenerate p⁺ type c-Si epitaxialgrowth layer (the opposite conductivity type degenerate c-Si layer) 71are formed in this order on the degenerate n⁺ type c-Si substrate (thefirst one conductivity type degenerate c-Si layer) 23 of 500 μm inthickness and resistivity of 1×10⁻³ Ω-cm by epitaxial growth is used.The fourth to the first non-degenerate n-type c-Si epitaxial growthlayer 41, 43, 45 and 47 are the epitaxial growth layer of 0.5 μm inthickness and resistivity of 5 Ω-cm respectively. Moreover, the third tothe first degenerate n⁺ type c-Si epitaxial growth layers 42, 44 and 46are the layers of 0.1 μm in thickness and resistivity of 1×10⁻³ Ω-cmrespectively, and the degenerate p⁺ type c-Si epitaxial growth layer 71are the epitaxial growth layer of 0.6 μm in thickness and resistivity of2×10⁻³ Ω-cm.

(b) Secondly, the aluminum electrode 65 is formed on the back of thedegenerate n⁺ type c-Si substrate 23 using a vacuum evaporation method.Moreover, sintering is performed at a predetermined temperature.

(c) Thereafter, as shown in FIG. 7, a container 1 having an opening onthe bottom, which is made of PTFE, is contacted closely with the surfaceof the c-Si wafer 9 using O-rings 2 to fill the anodizing mixed solutionconsisting of hydrofluoric acid and ethyl alcohol 4 into this containermade of PTFE 1. Since using the O-ring 2, the anodizing mixed solutionconsisting of hydrofluoric acid and ethyl alcohol 4 does not leak fromthe bottom of the container made of PTFE 1. The anodization solution 4consists of hydrofluoric acid of 50 weight percent and ethyl alcohol of99.9 weight percent mixed at a volume ratio of 1:1. In the anodizingmixed solution consisting of hydrofluoric acid and ethyl alcohol 4, aplatinum electrode 3 is arranged. The tungsten lamp 5 is arranged on theupper of the container made of PTFE. Moreover, the platinum electrode 3is arranged such that the light radiated from the tungsten lamp 5 cannot be impeded to reach the surface of the c-Si wafer 9.

(d) Subsequently, a desired anodizing current of 30 mA/cm² is fed forsix minutes through the anodizing mixed solution consisting ofhydrofluoric acid and ethyl alcohol 4 by the variable direct currentpower supply 6 connected between the platinum electrode 3 and thealuminum electrode 65. At the time, after adjusting the intensity of thelight irradiation such that the intensity of the light irradiation atthe surface of the c-Si wafer 8 becomes 20,000 lx, anodizing isperformed while irradiating with light by the tungsten lamp 5 arrangedon the upper of the container made of PTFE 1. As a result, the fourth tothe first non-degenerate n-type c-Si epitaxial growth layer 41, 43, 45and 47 become the fourth to the first n-type nanostructure PS layer 31,33, 35 and 37 respectively. Moreover, a part of the degenerate n⁺ typec-Si substrate 23 and the third to the first degenerate n⁺ type c-Siepitaxial growth layer 42, 44 and 46 become the fourth to the firstn-type mesostructure PS layer 13, 32, 34 and 36 respectively. Moreover,the degenerate p⁺ type c-Si epitaxial growth layer 71 becomes the p-typemesostructure PS layer 61.

(e) Thereafter, after the container made of PTFE 1 or the like aredetached, gold film is evaporated up to a thickness to show translucenceon the surface of the p-type mesostructure PS layer 61 using vacuumevaporation method or the like. Since the c-Si layer remains on theperiphery of the c-Si wafer 9 positioned outside an O-ring, theperiphery is cut and removed using a diamond blade or the like. Thus,the fundamental structure of the semiconductor light emitting deviceshown in FIG. 6 is completed. Moreover, a dicing and an assemblingprocesses thereafter are the same as the known process of thecommercially available crystalline LED, whereby the description isomitted. Moreover, the aluminum electrode 65 used as the contact atanodizing is used as the aluminum electrode 65. It is as a matter ofcourse that the aluminum electrode 65 used in anodizing is removed once,the conductive materials for the cathode 65 may be deposited newly.

As shown in FIG. 6, the structure that the fourth to the first n-typenanostructure PS layer 31, 33, 35 and 37 are connected sandwiching thethird to the first n-type mesostructure PS layer 32, 34 and 36 betweenthem, the series resistance Rs can be reduced as compared with thesemiconductor light emitting device having a single layer nanostructurePS layer of the same thickness as the total thickness of the four layersof the fourth to the first n-type nanostructure PS layer 31, 33, 35 and37. This is caused by that as is described using FIG. 3, the seriesresistance Rs of the n-type nanostructure PS layer is increased inproportion to the square of the thickness. That is, for example, theseries resistance Rs of the n-type nanostructure PS layer of 2 μm inthickness amounts to sixteen times of the series resistance Rs of thenanostructure PS layer of 0.5 μm in thickness. However, as shown in FIG.6, when the structure that the four layers of the n-type nanostructurePS layer of 0.5 μm in thickness are connected through the n-typemesostructure PS layer whose resistivity is low is taken, the entireseries resistance Rs .sub.(total) amounts to only approximate four timesof the single layer nanostructure PS layer of 0.5 μm in thickness.Generally, the entire series resistance Rs.sub.(total-div) of a stackedstructure that the N layers of the n-type nanostructure PS layer of d/Nin thickness are connected through the n-type mesostructure PS layer canbe reduced to approximate 1/N with respect to the entire seriesresistance Rs.sub.(total-single) of the single layer nanostructure PSlayer of "d" in thickness. It is the same as the case of the fistembodiment that when being made by the method as shown in FIG. 7, then-type nanostructure PS layers 31, 33, 35 and 37 whose EL efficiency arehigh are formed only on the portions of the original non-degeneraten-type c-Si layer 41, 43, 45 and 47, whereby the correct film-thicknesscontrol and the sufficient "transformation of crystalline silicon toporous silicon" are stimulated, whereby the luminescence efficiency ofthe nanostructure PS layer can be improved.

FIG. 8 shows a relationship between an external quantum efficiency and aseries resistance Rs of a semiconductor light emitting device (a symbolof O) according to a second embodiment of the invention. For comparison,FIG. 8 shows also relationships between an external quantum efficiencyand series resistance of a semiconductor light emitting device (a symbolof Δ) according to the prior art and the semiconductor light emittingdevice (a symbol of □) according to the first embodiment of theinvention.

The anodizing conditions of each of the semiconductor light emittingdevices (the symbol of O) according to the prior art, the first and thesecond embodiments of the invention are the same. Moreover, thethickness (2 μm) of the nanostructure PS layer 12 of the semiconductorlight emitting device according to the first embodiment of the inventionand the sum (0.5×4=2 μm) of the thickness of four layers of thenanostructure PS layers 31, 33, 35 and 37 of the semiconductor lightemitting device according to the second embodiment of the invention arethe same. Although the EL external quantum efficiency of eachsemiconductor light emitting device shown in FIG. 8 are approximatesame, in the respective series resistance Rs the significant differenceis recognized. That is, since the thickness of the semiconductor lightemitting devices according to the prior art shown by the symbol of Δ isthick as is 8 μm, the series resistance Rs is largest as is 150 k Ω. Incontrast with this, since the thickness of the nanostructure PS layer 12of the semiconductor light emitting device according to the firstembodiment of the invention shown by the symbol of □ can be controlledcorrectly to be thinned to 2 μm, the series resistance Rs is reduced to1/15 as is approximate 8 k Ω. Furthermore, the series resistance Rs ofthe nanostructure PS layer 12 of the semiconductor light emitting deviceaccording to the second embodiment of the invention shown by the symbolof O is 1.6 k Ω and is reduced to 1/5 as compared with the semiconductorlight emitting device according to the first embodiment, thus, thesmallest value is achieved. As described above, the reduction effect ofthe series resistance Rs of the nanostructure PS layer 12 of thesemiconductor light emitting device according to the second embodimentof the invention is apparent.

Third Embodiment

The PS layer can be made on the same c-Si substrate (wafer) to form asemiconductor integrated circuits (ICs). Therefore, the semiconductordevice according to the invention can be integrated readily into theoptoelectronic integrated circuits (OEIC) and the ICs such as a displaydevice for an image display, thereby being applicable to various fields.A selective diffusion technology may be used for integration. That is,when the multi-layer diffused region constituted by the degenerate c-Silayer and the non-degenerate layer on the predetermined portion of thePS wafer is selectively formed, the semiconductor device structureaccording to the invention can be formed locally on the portion of themulti-layer diffused region.

FIG. 9A is a schematic view of a display device in which the PS lightemitting diode (LED) array 101 of 512×512 dots is arranged on thecentral portion of the silicon wafer of 300 mm φ in diameter, and thecircuits such as a data driver 109 and a scan driver 115 for driving thePS light emitting diode (LED) array are formed on the periphery thereof.

FIG. 9B is a block diagram showing a constitution of a display deviceshown in FIG. 9A. This display device is a gradation control type LEDdisplay device for controlling a lighting period of the PS lightemitting diode (LED) arranged in a dot-matrix form. To the driver sideof the PS LED array 101, a data driver 109 is connected, and a scandriver 115 is connected to the scan side of the PS LED array 101. Thedisplay device shown in FIG. 9B further has a data input control circuit103, a RAM 105 connected to the data input control circuit 103, agradation control circuit 107 connected between the data driver 109 andthe data input control circuit 103. At the scan side, two-stage counter111a and 111b, a decoder 113 connected between the counter 111b and thescan driver 115 are provided.

The data input control circuit 103 fetches the predetermined displaydata and sends to the RAM 105 in synchronism with a clock signal CK1during the time period that a selection signal SE turns in "H". Forexample, the display data of 8 bits may be employed to represent onedot, to allow the light intensity of 255-step gradation for the one dot.When the stored 512 dots of 8 bits data of the RAM 105 are read, thedata are sent to the gradation control circuit 107. The gradationcontrol circuit 107 controls the lighting duration of every dot based onthe display data of 8 bits with 255-step gradation. The data driver 109drives the 512 dots of the LED 101a simultaneously based on the lightingduration gradation-controlled.

On the other hand, a signal which is sent from two-stage counter 111aand 111b which are reset by a reset signal Re and synchronizes with theclock signal CK1 is entered into the scan driver 115 via the decoder113. The scan driver 115 scans this 512 dots of the LED 101a in orderevery time the 512 dots of the LED 101a is driven by the data driver109.

FIG. 9C is a schematically sectional view showing two dots of the LEDmatrix 101. As shown in FIG. 9C, in the matrix section of a LED displaydevice according to a third embodiment of the invention, a n-type c-Siburied layer 14 is formed on a p-type c-Si substrate 83. On the n-typec-Si buried layer 14, the n-type mesostructure PS layer (the first oneconductivity type mesostructure PS layer) 13; the n-type nanostructurePS layer (the first one conductivity type nanostructure PS layer) 12 ofapproximate 1 to 2 μm in thickness; and the p-type mesostructure PSlayer (the opposite conductivity type mesostructure PS layer) 61 ofapproximate 0.6 to 1 μm in thickness are formed in order. The n-typec-Si buried layer 14, the n-type mesostructure PS layer 13, the n-typenanostructure PS layer 12 and the p-type mesostructure PS layer 61 areseparated by a element isolation region 86 and are formed as a pluralityof electrically independent regions, or LED dots. Plug electrodes 85penetrate the p-type mesostructure PS layer 61, the n-type nanostructurePS layer 12, the n-type mesostructure PS layer 13 and reach the n-typec-Si buried layers 14. The plug electrodes 85 serve as the cathodes ofthe respective LED dots 101a. This plug electrode 85 is formed by animpurity doped polysilicon (a doped polysilicon), refractory metals suchas tungsten (W), molybdenum (Mo), titanium (Ti), or refractory metalsilicides. Transparent electrodes 87 such as ITO films and SnO₂ filmswhich serve as the respective anodes of the LED 101a dots are formed onthe p-type mesostructure PS layers 61. The respective transparentelectrodes 87 are connected to a scanning line 96 constituted by metalssuch as aluminum or aluminum alloy and the respective plug electrodes 85are connected to data lines 89. The data line 89 also is constituted bymetals such as aluminum or aluminum alloy. The data lines 89 and thetransparent electrodes 87 are separated by first interlayer insulatingfilms 88, the scanning line 96 and the data lines 89 are separated bysecond interlayer insulating films 95.

According to such constitution, the display device that the PS LED array101 is arranged on the central portion of a large-diameter silicon waferand peripheral circuits such as the drivers of the PS LED array 101 arearranged around the periphery of the silicon wafer is formed readily.

The LED display device according to the third embodiment of theinvention can be manufactured as follows.

(a) First, the non-degenerate p-type c-Si layer of 500 μm in thicknessand resistivity of 10 Ω-cm to 2×10⁻² Ω-cm is formed by epitaxial growthon the degenerate n⁺ type c-Si substrate 23 of 300 mm diameter, 1 mm inthickness and resistivity of 1×10⁻³ Ω-cm. Moreover, a metal mask 131 forion implantation of approximate 1 μm in thickness is formed on a portionplanned to form the scan driver 115 and the data driver 109 around theperiphery of the c-Si substrate 23. As shown in FIG. 10A, arsenic (⁷⁵As⁺) is implanted with acceleration energy of 3 MeV, dose of 4×10¹⁶ cm⁻²using this mask 131. Furthermore, in order to compensate latticedistortion due to high concentration ion implantation, phosphorus (³¹P⁺) is implanted with acceleration energy of 2.5 MeV to 4 MeV, dose of4×10¹⁶ cm⁻² to perform heat treatment, thereby a degenerate n⁺ type c-Siburied layer being formed. Furthermore, as shown in FIG. 10B, phosphorus(³¹ P⁺) is implanted with acceleration energy of 0.8 MeV to 1.5 MeV,dose of 4×10¹³ cm⁻² to 4×10¹⁴ cm⁻² using the mask 131 to perform heattreatment, thereby a non-degenerate n-type c-Si layer 22 being formed.Furthermore, as shown in FIG. 10C, boron (¹¹ B⁺) is implanted withacceleration energy of approximate 50 kV, dose of 4×10¹⁶ cm⁻² using themask 131 to perform heat treatment. As a result, as shown in FIG. 10D,on the degenerate n⁺ type c-Si substrate 23, the degenerate n⁺ type c-Siburied layer 24, the non-degenerate n-type c-Si layer 22, and thedegenerate p⁺ type c-Si layer 71 are formed selectively on centralportion of the wafer;

(b) Subsequently, in the same manner as FIG. 5, the aluminum electrode65 is formed on the back of this degenerate n⁺ type c-Si substrate 23using a vacuum evaporation method or a sputtering method. Thereafter,sintering is performed at 400 to 450° C. to get better ohmic contact ofthe aluminum electrode 65 to reduce the contact resistance. Thereafter,as shown in FIG. 10E, a container 1 having an opening on the bottom,which is made of PTFE, is contacted closely with the surface of the 300mm c-Si wafer using O-rings 2. The O-ring 2 is arranged to be positionedalong the boundary between the LED array section and the peripheralcircuit section. Since the LED array section 101 is a quadrilateral, itis preferable that a quadrilateral shape window is opened on the bottomof the container made of PTFE 1. Accordingly, the O-ring 2 is guided bya O-ring groove so that the O-ring 2 is disposed quadrilaterally. Theanodizing mixed solution consisting of hydrofluoric acid and ethylalcohol is filled into this container made of PTFE 1, and the anodizingcurrent is fed for six minutes through the platinum electrode 3 and thealuminum electrode 65 (See FIG. 5). At the time, after adjusting theintensity of the light irradiation, anodizing is performed, whileirradiating with light. As a result, the degenerate p⁺ type c-Si layer71 becomes the p-type mesostructure PS layer 61. Moreover, a part of thedegenerate n⁺ type c-Si buried layer 24 also is anodized in the same wayto become the n-type mesostructure PS layer 13. The remained degeneraten⁺ type c-Si buried layer 24 becomes the degenerate n-type c-Si buriedlayer 14. On the other hand, the non-degenerate n-type c-Si layer 22becomes the n type nanostructure PS layer 12 by anodization, whereby thelaminated structure as shown in FIG. 10E is completed.

(c) Subsequently, an bonding insulating film 81 is formed by a CVDmethod on the p-type mesostructure PS layer 61 to finish the surfaceinto the a mirror surface by CMP method or the like. On the other hand,a 300 mm c-Si wafer 82 is prepared distinctly to finish the surface intoa mirror surface by CMP method or the like. Moreover, by bonding thesesurfaces each other, a Silicon Wafer Direct Bonding (SDB) substrate asshown in FIG. 10F is formed. Moreover, as shown in FIG. 10G, the back ofthis SDB substrate is ground and polished to make the thickness of thedegenerate n⁺ type c-Si substrate 23 thin to 2 to 10 μm (or by removingthe degenerate n⁺ type c-Si substrate 23, the n-type c-Si buried layer14 is allowed to be exposed). Hereinafter, the degenerate n⁺ type c-Sisubstrate 23 remained thinly is referred to as "the degenerate n-typec-Si buried layer 14". Moreover, the surface of the degenerate n-typec-Si buried layer 14 is finished into the mirror surface by CMP methodor the like.

(d) Furthermore, another c-Si wafer 83 of 300 mm diameter, 1 mm inthickness and resistivity of approximate 10 to 500 Ω-cm is prepared tofinish the surface into the mirror surface by CMP method or the like.Moreover, by bonding these surfaces each other, the SDB substrate asshown in FIG. 10H is formed. Now, the 300 mm c-Si wafer 82 directlybonded firstly is ground and polished to remove. Further the bondinginsulating film 81 is removed as shown in FIG. 10I.

(e) As shown in FIG. 10J, grooves 91 which penetrate the p-typemesostructure PS layer 61, the n-type nanostructure PS layer 12, then-type mesostructure PS layer 13 and reaches the n-type c-Si buriedlayer 14 is formed. Forming of the grooves 91 may be performed by RIE orECR ion etching employing CF₄, SF₆, CBrF₃, SiCl₄, or CCl₄ or the likeusing silicon oxide film as a mask. At this trench etching, it iseffective to cool the substrate at 110° C. to 130°.

(f) Moreover, as shown in FIG. 10K, an oxide film 84 is formed bythermal oxidation of the surface of the groove 91. Moreover, as shown inFIG. 10L, the oxide film 84 at the bottom of the groove 91 is removed bythe RIE excellent in a directivity. Thereafter, as shown in FIG. 10M,the doped polysilicons or refractory metals are embedded inside thegrooves 91 to form the plug electrodes 85. Furthermore, planarization ofthe surface is performed by the CPM method.

(g) Subsequently, as shown in FIG. 10N, an element isolation groove 92is formed through the p-type mesostructure PS layer 61, the n-typenanostructure PS layer 12, the n-type mesostructure PS layer 13 and then-type c-Si buried layer 14. Moreover, as shown in FIG. 10O, an elementisolation oxide film 86 is embedded into the element isolation groove92. Furthermore, planarization of the surface is performed by the CPMmethod.

(h) Thereafter, as shown in FIG. 10P, the transparent electrode 87 suchas the ITO film and the SnO₂ film is formed by the CVD method or asputtering method. Moreover, as shown in FIG. 10Q, the transparentelectrode 87 is separated at the positions of the respective dotsconstituting the matrix by the RIE method. After separation of thetransparent electrodes 87, the periphery circuit section such as thescan driver 115 and the data driver 109 is formed using processes for awell known MOS transistor or the like around the periphery of thedegenerate n⁺ type c-Si substrate 23. After forming polysilicon gateelectrodes of the circuits arranged on the periphery, as shown in FIG.10R, a first interlayer insulating films 88 such as the silicon oxidefilm, PSG film and BPSG film is formed on the polysilicon gate electrode(not shown) and the transparent electrode 87. Contact holes are openedin the first interlayer insulating films 88 and the data lines 89constituted by aluminum or aluminum alloy are formed to be connected tothe plug electrodes 85 as shown in FIG. 10S. Simultaneously, metalinterconnections required in the periphery circuit section are alsoformed. Moreover, a second interlayer insulating film 95 such as thesilicon oxide film, PSG film, BPSG film and Si₃ N₄ further is formed onthe data line 89 and the metal interconnections required in theperiphery circuit section. Contact holes are opened on this secondinterlayer insulating film 95, the scanning line 96 constituted byaluminum or aluminum alloy is connected to the transparent electrode 87,and the metal interconnections required in the periphery circuit sectionis formed, whereby the matrix section of the LED display deviceaccording to the third embodiment of the invention shown in FIG. 9C iscompleted. In FIG. 9C, although a final passivation film is omitted, asis well known to those skilled in art the passivation film may be formedas required.

Moreover, even without the use of the method as shown in FIG. 10F to10I, the structure that the n-type c-Si buried layer 14, the n-typemesostructure PS layer 13, the n-type nanostructure PS layer 12 and thep-type mesostructure PS layer 61 are formed in order on the p-type c-Sisubstrate 83 as shown in FIG. 10I can be realized. For example, first,the degenerate n⁺ type c-Si substrate 23, the non-degenerate n-type c-Silayer 22 and the degenerate p⁺ type c-Si epitaxial growth layer 71 areformed by epitaxial growth on the p-type c-Si substrate 83. Thereafter,as shown in FIG. 11, a groove which reaches the degenerate n⁺ type c-Sisubstrate 23 from the back of the p-type c-Si substrate 83 is opened toprovide the cathode to feed the anodizing current through the platinumelectrode 3. However, there is a risk that since the n-type c-Si buriedlayer 14 is thin, the resistivity of this portion is high, the anodizingbecomes non-uniform. Therefore, for a large wafer of approximate 300 mmin diameter, a SDB method as shown in FIG. 10F to FIG. 10I is preferablyused.

In the structure shown in FIG. 9C, since the element isolation oxidefilm 85 is transparent, there is a light leakage through the adjacentdots. Therefore, in order to obtain a sharp image, a shielding region142 as shown in FIG. 12 may be formed in the element isolation oxidefilm 85. Tungsten (W) may be used as the shielding region 142. In FIG.12, the light is designed to be emitted from the upper surfaceefficiently by further arranging a Bragg mirror 141 constituted byquarter-wave dielectric stacks on the lower of the n-type c-Si buriedlayer 14. The Bragg mirror 141 may be sandwiched between the n-type c-Siburied layer 14 and the p-type c-Si substrate 83 by the SDB process.

Moreover, the structure that the light is designed to allow to emittoward the lower of the wafer by removing the c-Si substrate 83 of thebottom of the LED array section by etching may be taken. In this case,since the non-degenerate n-type c-Si layer 22 and the degenerate p⁺ typec-Si layer 71 may be formed on the degenerate n⁺ type c-Si substrate of300 mm diameter by epitaxial growth to finally remove the degenerate n⁺type c-Si substrate of the lower of the LED array section by etching,the SDB method as shown in FIG. 10F to FIG. 10I is not required to use.However, there may be cambers, warps and drawbacks in mechanicalstrength due to the large area thereof, since the wafer is very thin.

Moreover, although in the above description, the description isperformed using the wafer of 300 mm (12 inches) in diameter as anexample of the large-diameter wafer, it is as a matter of course thatother wafer size such as 4 inches to 10 inches also may be used.

Other Embodiment

Various modifications will be possible for these skilled in the artafter receiving the teachings of the present disclosure withoutdeparting from the scope thereof.

For example, although in the first and the second embodiments describedabove, the case where the n-type nanostructure PS layer constituted byanodizing the non-degenerate n-type c-Si layer under light irradiationis used as the EL actve layer is described, reversing the conductivitytype of the c-Si layer, the p-type nanostructure PS layer constituted byanodizing the non-degenerate p-type c-Si layer may be used as a matterof course as the luminescence layer. In this case, it becomes thestructure that all the p-type/the n-type in the first and the secondembodiments are inverted. Moreover, since the non-degenerate p-type c-Silayer becomes the p-type nanostructure PS layer also by anodizationwithout light irradiation, the tungsten lamp 5 shown in FIG. 5 and FIG.7 can be omitted. Moreover, as shown in FIG. 3, since the value of theseries resistance Rs of the p-type nanostructure PS layer is increasedin proportion to the cube of the thickness of the p-type nanostructurePS layer, the multi-layer dividing effect becomes more significant bydividing into a plurality of thin layers shown in FIG. 2.

In the third embodiment, it has been shown that the inexpensive andlarge area light emitting device can be formed by the array using the PSLED dots arranged in a matrix form. If the PS layers are not dividedinto a plurality of pieces so as to form the dot matrix, the lightemitting device for interior illumination or the like that the entiresurface of the silicon wafer of 4 inches to 12 inches in diameter servesas the light emitting region can be provided. FIG. 13 shows a partialsection view of such light emitting device that the entire surface ofthe silicon wafer serves as the light emitting region. When theresistance of the translucent gold electrode is affected by enlargementof the area, electrode wirings 97 having a low resistivity may beprovided in the stripe shape on the transparent electrode 87 such as aITO film and a SnO₂ film on the p-type mesostructure PS layer 61 asshown in FIG. 12.

Thus, it is as a matter of course that the invention includes variousembodiments which are not described herein. Therefore, the technologicalscope of the invention is defined by only the following claims which isreasonable from the above description.

What is claimed is:
 1. A semiconductor light emitting devicecomprising:(a) a first one conductivity type nanostructure poroussilicon layer; (b) an opposite conductivity type mesostructure poroussilicon layer disposed on said first one conductivity type nanostructureporous silicon layer; and (c) a first one conductivity typemesostructure porous silicon layer disposed under said first oneconductivity type nanostructure porous silicon layer.
 2. Thesemiconductor light emitting device of claim 1, wherein a thickness ofsaid first one conductivity type nanostructure porous silicon layer isnot more than 2 μm.
 3. The semiconductor light emitting device of claim1, wherein a thickness of said first one conductivity type nanostructureporous silicon layer is not more than 0.5 μm.
 4. The semiconductor lightemitting device of claim 1, further comprisinga second one conductivitytype nanostructure porous silicon layer disposed under said first oneconductivity type mesostructure porous silicon layer; and a second oneconductivity type mesostructure porous silicon layer disposed under saidsecond one conductivity type nanostructure porous silicon layer.
 5. Thesemiconductor light emitting device of claim 4, wherein a thickness ofsaid first and second one conductivity type nanostructure porous siliconlayer is not more than 0.5 μm respectively.
 6. The semiconductor lightemitting device of claim 4, wherein said first one conductivity typenanostructure porous silicon layer, said opposite conductivity typemesostructure porous silicon layer, and said first one conductivity typemesostructure porous silicon layer are laminated on a central portion ofa silicon wafer, and a peripheral circuit is arranged on a remainingportion of the silicon wafer.
 7. The semiconductor light emitting deviceof claim 6, wherein said first one conductivity type nanostructureporous silicon layer, said opposite conductivity type mesostructureporous silicon layer, and said first one conductivity type mesostructureporous silicon layer are laminated on the central portion of the siliconwafer as a plurality of independent regions respectively, and elementisolation regions are arranged between each of a plurality ofindependent regions.
 8. The semiconductor light emitting device of claim7, wherein said a plurality of independent regions forms a matrix array,and peripheral circuit for driving the matrix array are arranged on saidremaining portion of the silicon wafer.
 9. The semiconductor lightemitting device of claim 1, further comprising a stacked structurehaving a plurality of one conductivity type nanostructure porous siliconlayer and a plurality of one conductivity type mesostructure poroussilicon layer laminated alternately, the stacked structure beingdisposed under said first one conductivity type mesostructure poroussilicon layer.